michigan_tech wrote:
To begin with, I found this post very helpful and it has a lot of great information on the whole. As far as using all of it, I will need some further clarification. |
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Thank you, and my apologies, all rolled up into one! My previous post might have been a bit vague. I will try to elaborate... I have the ideas in MY head, but that certainly doesn't put them into YOUR head!
michigan_tech wrote:
To begin with, what sort of microphone would you recommend implementing? Keep in mind budget and size if possible. Any model numbers and other specifications would be greatly appreciated. |
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The microphone you want will ideally have a VERY flat frequency response. The flatter the better, but you certainly would want to be within a 1dB window, full range. 1dB would be the minimum design parameter, as 1dB is generally accepted the minimum difference the ear can hear. Additionally, whatever your response variance at the mic, this will be amplified at each step along the chain...
Flatter is better.
I know that the microphone I use in all my testing is the Behringer ECM8000, A very flat response mic, it would be ideal, were it not for the shotgun shape. As a proof of concept, however, it would do quite well for you. At only 80 dollars retail, it's a fantastic step for you! Here's the home page:
http://www.behringer.com/ECM8000/index.cfm?lang=ENG
It is an electret microphone, so a power supply will be required. ±15v is optimal. Balanced also, so electrical noise becomes a "not-issue". Again, for "proof of concept"... Perfect.
michigan_tech wrote:
As far as the "operational" amplifier, what exactly are you defining as such? |
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Sometimes called a buffer, an op-amp uses VERY high impedance inputs, so their input frequency response is very flat. Here are the op-amps I used in my home crossovers:
http://www.futurlec.com/Linear/OPA2134PA.shtml
Additionally, they offer the option of inverting or non-inverting outputs, with the addition or removal of one ground point. Easy.
They are used in buffer stages, as the first gain stage from the mic to the speaker signal chain.
:::::::UPDATE/EDIT:::::::
While searching for this answer, I came across a new IC from National Semiconductor. This guy would be small enough to attach RIGHT TO the speaker, direct speaker drive, single ended voltage power supply, vanishingly low THD... Worth exploring as an avenue:
http://www.national.com/pf/LM/LME49600.html
michigan_tech wrote:
And then to the subsequent amplifier, I am confused to what you are referencing with this. As far as inverting the output, that part is a little easier but some clarification would be great, especially outputting WHAT output to WHAT input, and how does this relate to the rest of the speaker system? |
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Once the low-level is inverted, the amplifier driving the speaker will stay non-inverted. The design and phase of the entire system will have to keep in mind that the ultimate end result will be that the speaker outputs a signal that is 180° out of phase from but of equal amplitude to the cabin noise.
michigan_tech wrote:
I know amplifiers sometimes have a "phase" adjust, does this have anything to do with it? I know most of these types of amplifiers are aftermarket amplifiers, but for stock amplifiers in cars I don't think this option is available, but I could be wrong. |
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See my previous answer. Generally speaking the "phase" adjust is usually 0° or 180°, but this is normally only found on subwoofer amplifiers for better integration with the door or bass (as opposed to sub-bass) speakers. MUCH higher end amplifiers might also have a phase adjust, allowing a complete sweep from 0-180°. If more than that is necessary, one would simply invert the subwoofer's wiring, then re-adjust.
michigan_tech wrote:
As far as using a multiplexer in each corner, can you lead me to how I would implement it and in what fashion? Any models you are familiar with that offer great quality with a budget price? I know I am asking a lot, but I guarantee you this project will be vastly improved with everybody's help. |
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haemphyst wrote:
While searching for this answer, I came across a new IC from National Semiconductor. This guy would be small enough to attach RIGHT TO the speaker, direct speaker drive, single ended voltage power supply, vanishingly low THD... Worth exploring as an avenue:
http://www.national.com/pf/LM/LME49600.html |
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michigan_tech wrote:
I really appreciate all the time all of you are putting into this, as this technology could easily put our project over the top.
Thank you,
Anthony
EE-Michigan Tech |
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It's what we do!
I also am hoping that something comes of this for you! If you get an "A", be sure to mention our names! <grin>
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."